Fluidized bed combustion systems are presently used more and more due to the advantages over grate or dust combustion systems and because one can burn solid fuels in them, especially coal. Due to the relatively low combustion temperatures in the fluidized bed, (which are in the vicinity of approximately 800.degree. to 900.degree. C.), fluidized bed combustion is characterized by a relatively low emission of toxic substances, especially by a low generation of nitrogen oxide. Absorption agents to bind the sulfur oxides generated during combustion can be directly included into the fluidized bed and can be extracted, together with the ash, following the reaction with the sulfur oxides. An important additional advantage of fluidized bed combustion systems consists in the large range of the coal that may be utilized, i.e. especially ballast rich coal may be employed.
It is known to separate solid particles borne by flue gas with cyclones placed outside the fluidized bed combustion, or with swirling chambers configured directly above the fluidized bed, and, due to their high coal or coke component, to feed the particles back into the fluidized bed.
However, cyclones, and especially swirling chambers, are relatively complex.
An important additional disadvantage of known fluidized bed combustion systems can also be found in the fact that, depending on varying loads, it is impossible to configure the fuel feed or the combustion performance quickly and problem free.